Conventionally, a spatial distribution of a magnetic field (hereafter also referred to as “magnetic field distribution”) is utilized in various applications such as locating an abnormal electric current path in an electronic component or examining a disease part of a human body. In measurement of such a magnetic field distribution, a superconducting quantum interference device, a magnetoresistive sensor, or the like is used as a magnetic field sensor. The superconducting quantum interference device is also referred to as “SQUID element”.
Magnetic force microscopy (MFM) may also be used to obtain a magnetic field distribution. A magnetic field sensor formed by coating a sharpened silicon tip with a magnetic thin film is used for an MFM probe. Such a probe is also referred to as “magnetic probe”. Patent Literature (PTL) 1 proposes a structure of using a carbon nanotube magnetic probe as the MFM probe. PTL 2 describes a method of measuring a three-dimensional distribution of a magnetic field, an electric field, a thermal field, or the like in a three-dimensional free space.
In the method described in PTL 2, the Laplace equation which is a fundamental equation of a static magnetic field is exactly solved using, as a boundary condition, a two-dimensional magnetic field distribution and a two-dimensional distribution of the gradient of the magnetic field obtained in a specific measurement plane, thus calculating a three-dimensional magnetic field distribution in a free space around the measurement plane. The gradient of the magnetic field mentioned here means a gradient of a magnetic field in a direction normal to the measurement plane. The free space around the measurement plane includes both a three-dimensional space above the measurement plane and a three-dimensional space below the measurement plane.
With the method described in PTL 2, a structure of a source of a magnetic field (magnetic field source) can be imaged using magnetic field distribution measurement data obtained in an area away from the magnetic field source. The image showing the structure of the magnetic field source is available, for example, for medical diagnosis or electronic component failure analysis.
In the case of analyzing the magnetic field source in the space below the measurement plane, an electronic circuit and a mechanical component for signal processing for the magnetic field sensor are typically present in the space above the measurement plane. These are not an object to be measured, but are a magnetic field source.
In the method described in PTL 2, the distribution of the field can be exactly analyzed even in the case where magnetic field sources are included in both of the spaces above and below the measurement plane.